In the production of metals from ores, a smelting procedure using coke and a flux generally is practised, with liquid metal being tapped at intervals. These procedures require the use of high grade ores and high temperatures, and tend to emit noxious gases and particulate matter.
A particular metal recovered in this manner is chromium. Present practice requires the use of an ore having a chromium to iron ratio of at least 3 to 1 and attempts to use low grade chromite ores, of varying composition and having chromium to iron ratios typically 1 to 2:1, more typically 1.2 to 1.5:1, in smelting procedures have been unsuccessful.
High carbon ferrochrome alloys are used in steel making, containing typically 55 to 66% Cr, 7 to 8% C and the balance Fe, and conventionally are formed from high grade chromite ore using carbon as a reducing agent. Low carbon ferrochromium is produced from high grade ore and silicon chromium alloys as reducing agent. The present invention also makes it possible for the first time to form a substantially pure chromium carbide or a high carbon ferrochrome alloy from chromite ores for use as steel additives.
The present invention makes it possible for the first time to recover substantially pure chromium metal from chromite ores and concentrates without smelting and in particular to recover pure chromium metal from low grade chromite ores.